This invention relates to a friction brake assembly.
An adjustable lifting device employed in an automotive vehicle such as, for example, a seat-height adjustment, a window-glass lifter, a head-rest lifter or the like, generally employs a friction brake assembly of a design wherein a force exerted by the operation of a manipulatable element such as a control lever can be transmitted to a loaded element such as a seat bottom, a window glass or a head rest for the adjustment of the position thereof, but force exerted by the loaded element can not be transmitted reversely to the manipulatable element because of a frictional force acting on the loaded element to lock the latter in position.
The friction brake assembly of the type referred to above is disclosed in, for example, the Japanese Laid-open Patent Publication No. 56-124522, published Sept. 30, 1981. The prior art friction brake assembly disclosed in the above-mentioned publication is depicted in FIGS. 1(a) and 1(b) of the accompanying drawings in longitudinal sectional view and in cross-sectional view taken along the indicated lines A--A in FIG. 1(a), respectively.
Referring to FIGS. 1(a) and 1(b), the friction brake assembly is used in association with the seat-height adjustment in an automotive vehicle and comprises a brake drum 2 of a generally cup-like configuration secured to a seat assembly 1, and a cap member 4 mounted on the brake drum 2 for rotation relative thereto and having a hand-operated control lever 3 rigidly connected thereto for rotation together therewith. The brake drum 2 accommodates therein a connecting member 5 fixed to the cap member 4, a relay member 7 fixedly mounted on an adjustment axle 6 forming a part of the seat-height adjustment for the seat assembly 1, a pair of spaced engagement members 8 mounted on the relay member 7, a torsion spring 11 preloaded to allow turns of the coil of the spring 11 to tightly contact the inner peripheral surface of the brake drum 2 and having its opposite ends 9 engaged in radial sockets 10 defined in the respective engagement members 8, and a sector-shaped element 15 fitted to a support projection 12 of the relay member 7 by means of set screws 14 loosely extending through an arcuate slot 13 in the sector-shaped element 15.
In this prior art friction brake assembly now under discussion, the support projection 12 has an abutment face 16 defined therein for the engagement with one of the engagement members 8 whereas the sector-shaped element 15 has an abutment face 17 for the engagement with the other of the engagement members 8. In operation, when the hand-operated control lever 3 is turned above the adjustment axle 6, the connecting member 5 fast with the cap member 4 is engaged to the engagement members 8 to angularly move the latter a distance corresponding to a play between the abutment face 16 (or 17 depending on the direction of turn of the control lever 3) and the engagement members 8. After the engagement members 8 have been angularly moved the distance corresponding to the play to contact the abutment face 16 (or 17) with the torsion spring 11 consequently released, the support projection 12 is urged in the same direction as the direction of turn of the control lever 3 to cause the relay member 7 to rotate together with the adjustment axle 6.
The prior art friction brake device of the construction described above has been developed with a view to minimizing a composite play, including the plays required between the engagement members 8 and the associated abutment faces 16 and 17 for facilitating the release of the torsion spring 11 and the play which is required for facilitating the fabrication of the brake device, by the elimination of the last mentioned play. Specifically, this is said to have been accomplished by rendering the sector-shaped element 15 to be adjustably connecting to the support projection 12 by means of the adjustment screws 14 so that the position of the abutment face 17 relative to the associated engagement member 8 can be adjusted. However, as can readily be understood from FIGS. 1(a) and 1(b), the last mentioned play has not been completely eliminated and still remains relatively large and, therefore, the seat assembly is susceptible to a jolting motion of a magnitude corresponding to the size of the play.